Uktzin, Chapter 3, Mishnah 12. This is the final Mishnah in all of Shas. After six sedarim of halachah, after all the intricate discussions of tumah and taharah that fill this last masechta, the Tanna closes the Shisha Sidrei Mishnah not with another din but with two statements of aggadah: one about the reward waiting for those who learn, and one about the peace in which that reward, and everything else, is held.
The Mishnah opens with the words "Amar Rebbi Yehoshua ben Levi." His teaching is this: in time to come HaKadosh Baruch Hu will hand over to each and every righteous person, "kol tzaddik ve'tzaddik," an inheritance of three hundred and ten worlds, "shlosh me'os va'asarah olamos." The derivation comes from the pasuk "lehanchil ohavai yeish, ve'otzroseihem amalei": Hashem grants yeish as a portion to those who cherish Him, and their treasuries He will fill. In gematria the word "yeish" totals three hundred and ten, the shin being three hundred and the yud being ten. The number is thus embedded in the verse itself: three hundred and ten worlds for each tzaddik in Olam Haba.
The Rambam reads the word "yeish" as making a further point. There are those among the nations who hold that a person's existence simply comes to an end when he dies, and that is the whole of the story. The pasuk answers that claim with a single word: yeish, he still is, he continues to exist, and precisely because he continues to exist he is able to enjoy the great future that Olam Haba holds for him.
The Bartenura explains why this particular teaching was chosen to conclude the Torah Sheba'al Peh. Everything that came before was mitzvos and halachos and the toil of learning; the closing Mishnah assures us that there is schar, reward, for all of it, for every mitzvah performed and every piece of Torah acquired.
Why, though, does the Mishnah stress "every single tzaddik"? The Tosfos Yom Tov offers a beautiful answer. Anyone who has learned Mishnayos knows that one Tanna forbids where another permits; one holds a thing assur and his colleague is matir. Yet each of them was reaching for the truth, and the motive behind every opinion was lesheim Shamayim. Therefore the machmir and the meikil alike, the one whose shitah came out stringent and the one whose shitah came out lenient, are each called an ohev Hashem, and each is worthy of the reward the pasuk describes.
The Tiferes Yisroel adds another perspective. There rests upon us a great chiyuv of talmud Torah, to master the Shisha Sidrei Mishnah, and no one accomplishes that in a lifetime without surrendering a portion of his Olam Hazeh: comforts he could have had, pleasures he could have tasted, time he could have spent otherwise. A person can easily come to feel that he has spent his years sacrificing. The final Mishnah tells him otherwise. Whatever enjoyment this world could possibly have offered him does not begin to compare with the taanug ruchni, the spiritual delight, that awaits him in the world to come.
The Mishnah's second teaching is introduced with the words "Amar Rebbi Shimon ben Chalafta." His statement is that no container was found by HaKadosh Baruch Hu capable of holding berachah for Yisroel other than peace, "lo matza HaKadosh Baruch Hu kli machzik berachah l'Yisroel ella hashalom." He brings as proof the pasuk "Hashem oz l'amo yitein, Hashem yevarech es amo vashalom." The verse is speaking of kabalas haTorah: the oz, the might, that Hashem grants His nation is the Torah. And that identical verse concludes by telling us that Hashem blesses His people with shalom.
We meet this same design elsewhere. Shemoneh Esrei, when we arrive at its end, closes with the berachah of shalom; and the Torah follows the identical pattern, for our completion of the Shisha Sidrei Mishnah also arrives at shalom. Shalom is the container within which Klal Yisroel is bound together, and only inside that container can Torah grow and flourish.